Multi-stage turbine using steel and aluminum blades

ABSTRACT

A multistage turbine having one or more input stage fan blades formed of aluminum and having one or more output stage fan blades formed of steel. One or more intermediate stages may be formed of aluminum or steel or a combination thereof.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No. 60/862,384 filed Oct. 20, 2006, the entire contents of which are hereby expressly incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention is directed to turbines suited for application to paint sprayers, more particularly, to HVLP (High Volume, Low Pressure) type sprayers. Current turbine technology for HVLP paint spraying equipment uses aluminum blades for each stage of the turbine for turbines of between one and three stages. Steel blades are used for each stage of four stage turbines because of the higher pressures and temperatures present in the four stage version. Additionally, such higher performance turbines have been limited to 4 stages due to the large overhung load of the 4-steel blades. Because of the steel blade construction, these turbines are extremely difficult to balance. The extra weight changes the critical vibration frequency to be very close to the operating speed (RPM) of the turbine motor during normal operation. If the turbine is not properly balanced, the vibration harmonics can cause premature wear and even destroy the inboard bearing.

Each successive stage in a bypass turbine builds heat and pressure above the previous stages. Even though four stage turbines have found application in HVLP paint sprayer equipment, there continues to be a need for improved performance and reduced or controlled cost for turbines that exceed the performance of prior art four stage designs. A five (or more) stage turbine would be desirable, but making the stages out of steel would exacerbate the overhung load problem, and making the stages out of conventional aluminum is not feasible because the temperature and pressure at the outlet stage or stages of such a turbine design exceed the capability of conventional aluminum.

As used herein, conventional aluminum is to be understood to be non-aircraft grade aluminum, in contrast to aircraft grade aluminum which, typically, has one or more alloying elements added to change the characteristics of the aluminum. Of particular interest here are the various forms of aircraft grade aluminum which are able to withstand higher temperatures while maintaining sufficient strength in the intended application. Some examples of such alloying elements include: copper (in 2xxx series aluminum), magnesium and silicon (in 6xxx series aluminum), and zinc (in 7xxx series aluminum). Accordingly, as used herein, aircraft grade aluminum refers to those aluminum alloys which are capable of withstanding the high temperatures and pressures (loads) at the outlet stage(s) of HVLP turbines.

While aircraft grade aluminum may be suitable for the high temperatures and pressures at the outlet stage(s) of HVLP turbines, such materials have the disadvantage of increased cost over non-aircraft grade aluminum. (One example of non-aircraft grade aluminum is 1xxx series aluminum which has no major alloying element and has a minimum aluminum content of 99%.)

Aircraft grade aluminum has another disadvantage that it is not readily recyclable because of the presence of the alloying element(s). It is thus desirable to use non-aircraft grade aluminum in the inlet stage(s) of HVLP turbines with its cost and recyclable advantages, while avoiding the disadvantages of aircraft grade aluminum in the outlet stage(s) of such turbines.

BRIEF SUMMARY OF THE INVENTION

A simultaneous solution to both the critical frequency and overhung load issues for a five (or more) stage turbine is to make the first or inlet stages out of non-aircraft grade aluminum and the last or outlet stages out of steel. The first stages (the inlet stages) are the farthest outward from the intermediate bearing (located between the motor and fan section). Making the first stages of the fan section out of non-aircraft grade aluminum greatly reduces the overhung load, since such aluminum is roughly ⅓ the weight of steel. The higher (or outlet) stages that require a material to stand up to the increased pressure and temperature are located closer to the intermediate bearing so their weight is not as significant as it would be if located further away from the intermediate bearing.

The combination of steel blades at the outlet end and non-aircraft grade aluminum blades at the inlet end of the turbine is effective to place the steel blades at the region of the turbine having higher pressures and temperatures. The blades at the outermost end of the shaft that cause the most overhung load are made of non-aircraft grade aluminum where they are subjected to lower pressures and temperatures.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a perspective view of a prior art HVLP turbine assembly in its housing.

FIG. 2 is a view of the prior art turbine assembly and housing of FIG. 1, shown partly in section.

FIG. 3 is an exploded view of the prior art turbine assembly of FIG. 2.

FIG. 4 is a side view of a turbine of the present invention, cut away to illustrate certain aspects of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the Figures, and most particularly to FIGS. 1-3, a prior art HVLP turbine assembly 10 and housing 11 may be seen. In apparatus 10, a single stage reverse axial flow turbine 40 is close coupled to a four stage conventional flow tangential discharge turbine 41. The arrangement shown in FIGS. 1-3 is from U.S. Pat. No. 5,639,222, the entire contents of which are hereby expressly incorporated by reference. As may readily be noted, apparatus 10 is capable of providing a five stage turbine, but requires two motors (46 and 47), and is generally less efficient and more costly than an integral five stage fan section driven by a single motor.

FIG. 4 shows an integral five stage turbine 200 illustrating the present invention. Turbine 200 has a fan stage 210 and an electric motor 212 coupled to the fan stage 210 to drive the fan stage 210 through rotation of a motor shaft 214. Shaft 214 is preferably supported by a motor bearing 216 and an intermediate bearing 218. The rotating fan blades in fan stage 210 are positioned outboard of the intermediate bearing 218 and thus constitute an overhung load on shaft 214.

The first and second stage fan blades 220 are preferably made of non-aircraft grade aluminum. The third stage fan blade may be made of non-aircraft grade aluminum (or steel if desired). The fourth and fifth stage fan blades 224 are preferably made of steel. It is to be understood that the present invention may be extended to turbines with more stages, for example, six stages.

In operation, cooling air for motor 212 is drawn in along arrow 226 via motor air intake 228. The motor cooling air exits motor 212 in the direction of arrows 230. Turbine air enters a fan stage inlet 232 indicated by arrow 234, and exits the fan stage 210 via a tangential exhaust 236, in the direction of arrow 238.

The invention may thus be seen to be a multistage turbine having at least one inlet stage fan blade formed of non-aircraft grade aluminum, and one or more intermediate stage fan blade formed of non-aircraft grade aluminum or steel (or a combination thereof), and one or more outlet stage fan blades formed of steel.

In a preferred embodiment, the invention is a five stage turbine having a first stage fan blade and a second stage fan blade each formed of non-aircraft grade aluminum, and a third stage fan blade formed of at least one of steel and non-aircraft grade aluminum, and a fourth stage fan blade and fifth stage fan blade formed of steel.

It is to be understood that the intermediate stage fan blade may be formed of both aluminum and steel, if desired, for its various components.

It is to be further understood that the present invention may be practiced using aircraft grade aluminum for some or all of the aluminum parts of the present invention, with the consequent reduction or elimination of the advantages of using non-aircraft grade aluminum.

The invention is not to be taken as limited to all of the details thereof as modifications and variations thereof may be made without departing from the spirit and scope of the invention. 

1. A multistage turbine having at least one inlet stage fan blade formed of aluminum, and an intermediate stage fan blade formed of one of the materials of aluminum and steel, and an outlet stage fan blade formed of steel.
 2. The multistage turbine of claim 1 wherein the intermediate stage fan blade is formed of both aluminum and steel.
 3. The multistage turbine of claim 1 wherein at least the one inlet stage fan blade is formed of non-aircraft grade aluminum.
 4. The multistage turbine of claim 1 wherein the at least one inlet fan blade is formed entirely of aluminum.
 5. The multistage turbine of claim 1 wherein the aluminum is non-aircraft grade aluminum.
 6. A five stage turbine having a first stage fan blade and a second stage fan blade each formed of aluminum, and a third stage fan blade formed of at least one of steel and aluminum, and a fourth stage fan blade and fifth stage fan blade formed of steel.
 7. The turbine of claim 6 wherein the third stage fan blade is formed of both aluminum and steel.
 8. The turbine of claim 6 wherein at least the first and second stage fan blades are formed entirely of aluminum.
 9. The turbine of claim 6 wherein the aluminum is non-aircraft grade aluminum.
 10. The turbine of claim 6 wherein at least the first and second stage fan blades and the third stage fan blade are each formed of non-aircraft grade aluminum.
 11. The turbine of claim 6 wherein each fan blade formed of aluminum is formed of non-aircraft grade aluminum.
 12. A High Volume Low Pressure turbine assembly having five stages delivering air to a paint spray gun atomizing paint, the turbine assembly comprising: a) a plurality of inlet stage fan blades formed of non-aircraft grade aluminum; and b) at least one outlet stage fan blade formed of steel.
 13. The turbine assembly of claim 12 further comprising at least one intermediate stage fan blade formed of one of non-aircraft grade aluminum and steel.
 14. The turbine assembly of claim 12 further comprising at least one intermediate stage fan blade formed of both non-aircraft grade aluminum and steel. 